Dual role of PDMS on improving supercritical CO2 foaming of polypropylene: CO2-philic additive and crystallization nucleating agent

A systematic study was done to screen for the polydimethylsiloxane (PDMS) with molecular weight (Mw) from 770 g/mol to 17,000 g/mol to optimize the supercritical CO2 foaming process of semi-crystalline polypropylene (PP). The solubility and diffusion measurements demonstrated that the high solubility and slow desorption rate of CO2 were achieved in PP/PDMS blends via incorporating PDMS. Rheology results showed the viscosity of PP/PDMS blends increased with the increase of Mw of PDMS. The crystallization behaviors of PP and PP/PDMS blends were thoroughly investigated in the presence of CO2. PDMS with Mw from 4000 g/mol to 9000 g/mol enhanced the crystallization of the blend evidently. Since PDMS with medium Mw could work as a CO2-philic additive and crystallization nucleating agent in PP, the resultant foams exhibited a more uniform cellular morphology with smaller cell size (decreased from 23 to 13 mu m) and higher cell density compared with that of PP foam. (C) 2020 Elsevier B.V. All rights reserved.